JPH11312961A - Ramp wave control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the cost of an AGC circuit by increasing a constant current only when necessary and reducing a pull-in time. SOLUTION: In addition to a first comparator circuit 3, a second comparator circuit 4 for outputting only when the sample voltage of a ramp wave differs from its reference voltage by more than a specified value is provided, and an adjustment capability of the first comparator circuit is increased by adding the output of the second comparator circuit 4 to an operation current source of the first comparator circuit 3. As it is made possible to increase a pull-in capability by the second comparator circuit 4 only when necessary, it is possible to reduce the pull-in time of a ramp wave generation circuit at the time of supplying power or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control circuit for a ramp wave, and more particularly to a control circuit for a ramp wave generation circuit for controlling a scanning signal of a CRT or the like used in a television receiver or a display device of a computer.

[0002]

2. Description of the Related Art A ramp signal is used as a vertical deflection signal of a television receiver or a display device of a computer, and has a waveform shown in FIG. As the voltage of the ramp signal rises from the base voltage, the electron irradiation position is scanned, for example, from top to bottom. When the electron voltage reaches a predetermined voltage, the electron irradiation position falls again to the base voltage, and the irradiation position returns to the base position. Therefore, when the magnitude of the ramp wave changes, the size of the screen changes. Therefore, in order to keep the size of the screen constant, it is necessary to keep the peak value (peak) of the ramp signal constant.

An AGC (Auto Gain Control) circuit is used as a circuit that keeps the lamp signal constant. For example, a circuit shown in FIG. 4 can be considered. The ramp generation circuit 51 is a circuit for generating a ramp signal, outputs the ramp signal to an image display device (not shown),
Measure and output the ramp signal voltage at t (hereinafter referred to as sample voltage). The sample voltage is applied to the comparison
Is input to one of the input terminals. The comparison circuit 52 is a circuit that performs an output according to the difference between the two voltage inputs, and as shown in FIG. 4, combines a differential amplifier circuit 52a connected to a power supply voltage (Vcc) and a current mirror circuit 52b. Configuration. The comparison circuit 52, a constant current I ₀ is supplied from the operating current source connected to the power supply voltage Vcc. The other input terminal of the comparison circuit 52 receives the reference voltage of the ramp signal at the predetermined timing. If the sample voltage and the reference voltage are equal, the two transistors 5 of the differential amplifier 2a
Since an equal voltage is applied to the base electrodes of 2a 'and 52a ", an equal current 1 is applied to transistors 52a' and 52a".
/ 2 · I ₀ flows. The current mirror circuit 52b is a circuit in which the same current flows through the two transistors 52b 'and 52b''. Therefore, when the sample voltage is equal to the reference voltage, no output current is generated from the comparison circuit 52. If there is a difference between the sample voltage and the reference voltage, the transistor 52
Different currents for a 'and 52a''(eg, 1/2 · I ₀ + △
I flows, and 1 / 2aI _0- △ I flows through 52a ″).
(At this time, the sum of the currents flowing through the transistors 52a 'and 52a''becomes _I0 .) An equal current flows through the two transistors 52b' and 52b '' of the current mirror circuit 52b (for example, in the above example). In this case, 52b 'and 52b''are 1/2
・ I _0- △ I flows), so that the transistors 52a ′ and 52b ′
(For example, 2 △ I in the above example) cannot flow through the current mirror circuit 52b and becomes the output of the comparison circuit 52. The output of the comparison circuit 52 is connected to a first capacitor 53 connected to a power supply voltage, a second capacitor 54 grounded, and a ramp generation circuit 51. The output current of the comparison circuit 52 flows into the first and second capacitors 53 and 54, and the electric charge is accumulated, and becomes a potential corresponding to the output of the comparison circuit 52. This potential becomes the control voltage of the ramp generation circuit 51, and changes the magnitude of the ramp signal in the next and subsequent cycles. The output of the comparison circuit 52 is
The signal is output every cycle while the sample voltage and the reference voltage are equal, and the peak value of the ramp wave is kept constant.

[0004]

THE INVENTION Problems to be Solved] Conventional AGC circuits, capacitor 53 and capacitor 5 by distributing the constant current I ₀ supplied from the operating current source operation amplifier 52a
Since adjusting the fourth potential, the maximum potential difference conventional AGC circuit can be adjusted at one time is dependent on the magnitude of the constant current I _0. In the conventional AGC circuit, if the difference between the sample voltage and the reference voltage becomes larger than a certain value, it cannot be adjusted in one cycle. In other words, if I ₀ is small, the time until the ramp signal becomes the reference of the waveform, so-called pull-in time is longer.

[0005] To address this, by setting a large constant current I ₀ would be to easily conceivable, increasing the constant current I _0, too sensitive output of the comparator circuit, also, Since it becomes weak against noise, the waveform of the ramp is distorted as a result of adjusting the peak value. Therefore,
Setting a large constant current I ₀ is not intended to be adopted.

Further, the conventional AGC circuit has a small I ₀ , so that the pull-in time is as short as possible.
3 and a capacitor 54 are provided. This is because the reference voltage of the ramp wave is close to 1/2, 1/2 Vcc of the power supply voltage, and therefore, by providing the capacitor 53 connected to the power supply voltage Vcc and the grounded capacitor 54, the reference voltage at power-on is provided. It is provided to input 1/2 Vcc to the AGC circuit. Therefore, these two capacitors 53 and 54 are
If the pull-in time is sufficiently short, there is no functional problem in either one. In other words, the long pull-in time required two capacitors, thus leading to an increase in cost.

[0007] The present invention has been made in view of the challenges described above, the constant current I ₀
An object of the present invention is to increase the size of the AGC circuit only when necessary, shorten the pull-in time, and thereby reduce the cost of the AGC circuit.

[0008]

According to the present invention, there is provided a second comparison circuit for inputting to a first comparison circuit, and the first comparison circuit is provided only when a difference between a sample voltage and a reference voltage exceeds a predetermined value. In this case, the adjustment function is increased to temporarily increase the pull-in capability.

[0009]

FIG. 1 shows a conceptual diagram of an embodiment of the present invention. The ramp generation circuit 1 generates a ramp by changing the magnitude of the ramp in accordance with the voltage stored in the control voltage capacitor 2 and outputs the generated ramp to an image display device (not shown). Further, the ramp generation circuit 1 measures the voltage of the ramp wave to be output at a predetermined timing, and inputs the measured voltage to the first input terminal of the first comparison circuit 3 as a sample voltage. To the other input terminal of the first comparator circuit 3 reference voltage of the sample voltage is input, the first comparator circuit 3, according to the difference of the constant current I ₀ to the maximum value, the sample and reference voltages The output current is stored in the capacitor 2 and the magnitude of the ramp wave output from the ramp generation circuit 1 changes. The above is the same as the conventional technology.

[0010] The sample voltage and the reference voltage are also input to the input terminal of the second comparison circuit 4. Second comparison circuit 4
When the difference between the sample voltage and the reference voltage is larger than a predetermined reference, the constant current I ₀ ′ is output to the gate circuit 5 with the difference being the maximum value. The gate circuit 5 opens a gate according to the magnitude of the output of the second comparison circuit 4,
The current I ₂ flows to the first comparison circuit 3. As a result, the maximum value of the output current of the first comparator circuit is the sum of the constant current I ₀ and the current I _2, since the amount of current that is accumulated at one time in the capacitor 2 is increased, the control of the ramp control circuit Ability temporarily improves.

Next, a specific circuit example of the embodiment of the present invention will be described. FIG. 2 shows a circuit diagram of one embodiment of the present invention. The regions indicated by the dashed thin-line rectangles are regions corresponding to the first comparison circuit 3, the second comparison circuit 4, and the gate circuit 5 in FIG. 1, respectively.

The configuration of the first comparison circuit 3 is the same as that of the prior art, so that the details are omitted.

The second comparison circuit 4 is supplied with a constant current I ₀ ′, and comprises a differential amplifier and two constant current sources 4a. Similarly to the first comparison circuit 3, currents totaling I ₀ ′ flow through the two transistors of the differential amplifier according to the difference between the sample voltage and the reference voltage. By the way, the two constant current sources constitute a current mirror circuit (not shown).
While some work to be shed I _1, a large current does not flow from the constant current I _1. Within difference predetermined range of the reference voltage and the sample voltage, the current flowing through the two transistors of the differential amplifier will enter in equilibrium within a predetermined range, the magnitude of current flowing through one transistor is smaller than I ₁ Therefore, there is no output from the second comparison circuit 4. Then, the difference between the sampled voltage and the reference voltage becomes larger than the predetermined, the current flowing to either of the transistors of the differential amplifier exceeds I _1, as a current that can not flow into the constant current source output of the second comparator circuit Input to the gate circuit 5.

The gate circuit 5 is composed of two transistors 5a whose emitters are grounded, and a current mirror circuit 5b. The input of the gate circuit 5 is connected to the base electrodes of two transistors, one transistor of the current mirror circuit is connected to two grounded transistors, and the other transistor of the current mirror circuit 5b is connected to the current mirror. This is the output of the circuit 5. Second comparison circuit 4
, One of the two grounded transistors 5a of the gate circuit 5 is turned on. Then
Current mirror circuit 5 connected to these two transistors
Since current flows through the b, the gate circuit 5 outputs a current I _2.

[0015] Since the output from the gate circuit 5 is connected to the first comparator circuit 3, the maximum value of the output of the first comparator circuit to the sum of the output I ₂ of the constant current I ₀ and the gate circuit 5 Become.

Therefore, the ramp control circuit of the present embodiment can increase the maximum value of the output of the comparison circuit 3 only when the difference between the sample voltage and the reference voltage exceeds a predetermined value.

[0017]

According to the present invention, the pull-in capability can be increased only when necessary by the second comparison circuit, so that the pull-in time of the ramp generation circuit at the time of turning on the power can be shortened.

In order to shorten the pull-in time, capacitors 53 and 5 which are connected to the power supply voltage and the ground, respectively, are used.
4 can be reduced to one capacitor 2. The AGC circuit is generally an integrated circuit (IC) and is manufactured integrally, while the capacitors 53, 54 and 2 require a large capacitance to serve to regulate the control power of the AGC circuit, and It is an external component that cannot be built inside, but is connected using wiring outside the IC. Therefore, even if the second comparison circuit is increased, the manufacturing cost of the IC hardly changes. On the other hand, the cost can be reduced by reducing the number of external capacitors. Is reduced.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a ramp control circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a ramp wave control circuit according to the embodiment of the present invention.

FIG. 3 is a diagram showing a waveform of a ramp wave.

FIG. 4 is a circuit diagram of a conventional ramp wave control circuit.

Claims (3)

[Claims] And 1. A control voltage ramp generator for outputting a sample voltage is the voltage value of the predetermined timing of the ramp and ramp in accordance with the supplied constant current I _0, the sample voltage and the sample voltage A first comparison circuit that receives a reference voltage that is a reference value and outputs a current in accordance with a difference between the sample voltage and the reference voltage; and stores a ramp wave by storing an output of the first comparison circuit. A capacitor that fluctuates the control voltage of the generating circuit and a constant current I ₀ ′ are supplied,
A second comparison circuit to which the sample voltage and the reference voltage are input and output a current when a difference between the sample voltage and the reference voltage exceeds a predetermined value; and an output current of the second comparison circuit. And a gate circuit that outputs a current I ₂ while the input is present, wherein the current I ₂
Is added to the constant current I ₀ supplied to the comparison circuit of
A ramp wave control circuit for maintaining the magnitude of the ramp wave output from the ramp wave generation circuit constant by increasing the maximum value of the output current of the comparison circuit. Wherein said second comparator circuit according to claim 1, characterized in that it comprises a pair of transistors constituting the differential amplifier, a constant current source for supplying a constant current I ₁ that is connected to each of the transistors Ramp wave control circuit. 3. The gate circuit includes a transistor whose emitter is grounded, and a mirror circuit connected to the transistor. An input to the gate circuit is input to a base of the transistor whose emitter is grounded. The current I2 output from the circuit is output from a mirror circuit connected to the transistor, and the magnitude of the current I2 is
The ramp wave control circuit according to claim 1, wherein the control circuit changes according to a magnitude of an input to the gate circuit.